Floating facilities require anchors to resist uplift forces due to mooring and environmental loading. Whilst driven piles were initially used to anchor floating installations, difficulties in operating pile hammers precludes this option in deep water. The majority of floating facilities in deep water are moored using either drag anchors, suction caissons, suction embedded plate anchors or dynamically installed “torpedo piles”.
Recent innovation means that drag anchors can now withstand the high vertical loads dominant in taut-leg moorings. Furthermore the low mass and size of these anchors mean that an entire anchor suite can be transported to site on a single vessel. However, two major issues remain with the installation of drag embedded vertically loaded anchors.                1. The first issue relates to the drag length of the anchor during installation. This issue is becoming particularly crucial as the industry moves into deeper water as the drag distance increases with water depth, heightening the risk of interference with seabed infrastructure such as pipelines and increasing the need for alternative means of dealing with the excessive amounts of chain and wire required on the anchor handling vessel.        2. The second issue is the sub seabed trajectory of the anchor during installation. This issue is also critical as it dictates the final position and depth of the anchor, and in turn the anchor capacity. As a result, many of the installations involving vertically loaded anchors have necessitated a trial and error approach, resulting in prolonged anchor installation durations and hence costs.        
The foregoing difficulties in installing vertically loaded anchors have resulted in renewed interest in the use of suction caissons for deep water installations. They are advantageous as they are capable of withstanding high vertical loads and their position and embedment are readily controlled during installation. However, relative to drag anchors, suction caissons are expensive and of large size and weight, resulting in transportation and deployment problems.
Suction caissons have also been used as a means of installing plate anchors that are similar to the vertically loaded drag anchor referred to previously. In this application, commonly referred to as a Suction Embedded PLate Anchor or SEPLA, the caisson is used to embed an initially vertical plate anchor, located at the caisson base. When the system has reached the design embedment depth, the plate anchor mooring line is disengaged from the caisson, leaving the caisson free to be retrieved and reused for the next installation. At this point the plate anchor is vertically embedded in the seabed. The mooring line attached to the embedded plate anchor is tensioned, causing the plate anchor to rotate or ‘key’ to an orientation that is perpendicular to the direction of loading. The SEPLA has particular advantages over the suction caisson in that only one caisson is required for the installation process, reducing costs associated with procurement and transportation. However the installation process is still quite involved, requiring the use of pumps to pump water from the interior of the caisson during installation and remotely operated vehicles. These costs are also quite dependent on water depth, making them a less attractive solution for deep water applications.
WO 98/49048 and WO 00/26081 disclose a drag embedment anchor mounted at a lower end of a heavy elongate follower for deployment. The follower with the anchor attached is lowered from a vessel to the seabed. The anchor is then forced into the seabed to a desired depth by the weight of the heavy follower. The follower is then detached and removed leaving the anchor embedded in the seabed.
WO 2004/011327 discloses a method and device for deployment of a sheet anchor. The sheet anchor is mounted at a lower end of a pile which is lowered to the seabed and driven into the seabed by a vibratory hammer, or the like. After deployment of the anchor in the seabed the pile is removed from the sheet anchor.
Dynamically installed anchors, often referred to as torpedo piles, are an economical means of installing anchors in deep water. Dynamically installed anchors are released from a predetermined height above the seabed and rely on their self weight and the kinetic energy gained during freefall to self-bury in the seabed sediments. As no mechanical intervention is required during installation, installation costs are relatively independent of water depth. However these anchors can be extremely large and heavy with overall lengths of up to 22 meters and masses of over 100 tonnes. Hence fabrication and transportation costs can be very high. Furthermore, compared with other anchor types such as plate anchors, they are relatively inefficient at resisting vertical loads and tend to be susceptible to “setup” effects where the anchor capacity can only be realised after a significant period of time after installation has elapsed.
The present invention is directed towards overcoming these problems.